. The formation of microdroplet formulations of a drug, means of improving tissue compatibility and providing sustained release, involves the preparation of microspheres (O.1 micron diameter) of a drug-containing oil phase and encapsulation of them with a layer of phospholipid. A rat model will be used to test the microdroplet technology-based sustained delivery of azidothymidine which is intended to provide up to one week treatment regimen for HIV infection. A series of microdroplet formulations containing different concentrations of azidothymidine will be prepared in at least three tissue-compatible and FDA approved synthetic oils.The drug release kinetics of the AZT-containing microdroplets will be tested in an in vitro model as well as by intradermal and intramuscular injections into rats. A formulation which provides acceptable (zero order) release kinetics over a period of one week will be identified for further development in a Phase II SBIR proposal.